Peruvian Guano. 
193 
The Solubility of Phosphates in Guano. 
Genuine Peruvian guano contains from 22 to 24 per cent, of 
earthy phosphates ; but since the action of rain or other deterio- 
rating influences removes the soluble constituents, the proportion 
of insoluble or earthy phosphates is larger in inferior samples. 
The earthy phosphates occur in guano in a finely divided 
condition, in which they are no doubt more valuable than they 
would be in the shape of a coarse powder ; but several direct de- 
terminations have shown me that they are not more soluble than 
good bone-dust. 
In two experiments which I made, I found that 1 gallon of 
water dissolved respectively 246 and 2 - 64 grains of phosphate of 
lime. 
In addition to insoluble phosphate of lime and magnesia 
(bone-earth), guano, it will be seen by the preceding analyses, 
contains soluble phosphoric acid in considerable though varying 
quantities. The soluble phosphoric acid occurs naturally as 
phosphate of ammonia, which, according to the usual way of 
performing an analysis, is classed with the alkaline salts. As 
this phosphoric acid is a most valuable constituent, it ought 
always to be determined when it is desired to ascertain correctly 
the money-value of guano. On an average I find in Peruvian 
guano a quantity of soluble phosphoric acid, which corresponds 
to 5 to 6 per cent, of bone-earth. 
Alkaline Salts. — In considering the value of Peruvian guano, 
the fact that it contains potash ought not to be overlooked. 
On an average good samples contain from 6 to 8 per cent, of 
alkaline salts, and, according to Professor Way, nearly one half 
of their weight consists of potash. 
This constituent may contribute a good deal to its value as a 
manure for root-cops grown on light land deficient in potash. 
Salt does not fix Ammonia. 
Various means of increasing the efficacy of guano have been 
from time to time recommended, amongst others the addition of 
salt ; and there can be no doubt of the propriety of such an ad- 
mixture. The grounds on which its recommendation was based 
are, however, mistaken, because the beneficial effect certainly 
does not arise from any power which salt is supposed to possess 
of fixing the ammonia. Any one, who possesses even a slight 
acquaintance with chemistry may readily ascertain experimentally 
the amount of free .ammonia contained in solutions or dry sub- 
stances, and may satisfy himself that free ammonia is neither 
increased nor diminished by the addition of salt in small or 
large quantities. It is strange how generally the opinion has 
